The present invention relates generally to the field of digitally controlled ink jet printing systems. It particularly relates to improving those systems that asymmetrically heat a continuous ink stream, in order to deflect the stream""s flow between a non-print mode and a print mode.
Ink jet printing is only one of many digitally controlled printing systems. Other digital printing systems include laser electrophotographic printers, LED electrophotographic printers, dot matrix impact printers, thermal paper printers, film recorders, thermal wax printers, and dye diffusion thermal transfer printers. Ink jet printers have become distinguished from the other digital printing systems because of the ink jet""s non-impact nature, its low noise, its use of plain paper, and its avoidance of toner transfers and filing.
The ink jet printers can be categorized as either drop-on-demand or continuous systems. However, it is the continuous ink jet system which has gained increasingly more recognition over the years. Major developments in continuous ink jet printing are as follows:
Continuous ink jet printing itself dates back to at least 1929. See U.S. Pat. No. 1,941,001 which issued to Hansell that year.
U.S. Pat. No. 3,373,437, which issued to Sweet et al. in March 1968, discloses an array of continuous ink jet nozzles wherein ink drops to be printed are selectively charged and deflected towards the recording medium. This technique is known as binary deflection continuous ink jet printing, and is used by several manufacturers, including Elmjet and Scitex.
U.S. Pat. No. 3,416,153, issued to Hertz et al. in December 1968. It discloses a method of achieving variable optical density of printed spots, in continuous ink jet printing. Therein the electrostatic dispersion of a charged drop stream serves to modulate the number of droplets which pass through a small aperture. This technique is used in ink jet printers manufactured by Iris.
U.S. Pat. No. 4,346,387, also issued to Hertz, but it issued in 1982. It discloses a method and apparatus for controlling the electrostatic charge on droplets. The droplets are formed by the breaking up of a pressurized liquid stream, at a drop formation point located within an electrostatic charging tunnel, having an electrical field. Drop formation is effected at a point in the electric field, corresponding to whatever predetermined charge is desired. In addition to charging tunnels, deflection plates are used to actually deflect the drops.
Until recently, conventional continuous ink jet techniques all utilized, in one form or another, electrostatic charging tunnels that were placed close to the point where the drops are formed in a stream. In the tunnels, individual drops may be charged selectively. The selected drops are charged and deflected downstream by the presence of deflector plates that have a large potential difference between them. A gutter (sometimes referred to as a xe2x80x9ccatcherxe2x80x9d) is normally used to intercept the charged drops and establish a non-print mode, while the uncharged drops are free to strike the recording medium in a print mode as the ink stream is thereby deflected, between the xe2x80x9cnon-printxe2x80x9d mode and the xe2x80x9cprintxe2x80x9d mode.
Recently, a novel continuous ink jet printer system has been developed which renders the above-described electrostatic charging tunnels unnecessary. Additionally, it serves to better couple the functions of (1) droplet formation and (2) droplet deflection. That system is disclosed in our copending U.S. Pat. No. 6,079,821 entitled xe2x80x9cCONTINUOUS INK JET PRINTER WITH ASYMMETRIC HEATING DROP DEFLECTIONxe2x80x9d. Therein disclosed is an apparatus for controlling ink in a continuous ink jet printer. The apparatus comprises an ink delivery channel, a source of pressurized ink in communication with the ink delivery channel, and a nozzle having a bore which opens into the ink delivery channel, from which a continuous stream of ink flows. A droplet generator inside the nozzle causes the ink stream to break up into a plurality of droplets at a position spaced from the nozzle. The droplets are deflected by heat from a heater (in the nozzle bore) which heater has a selectively actuated section, i.e. a section associated with only a portion of the nozzle bore. Selective actuation of a particular heater section, at a particular portion of the nozzle bore produces what has been termed an asymmetrical application of heat to the stream. Alternating the sections can, in turn, alternate the direction in which this asymmetrical heat is applied and serves to thereby deflect the ink droplets, inter alia, between a xe2x80x9cprintxe2x80x9d direction (onto a recording medium) and a xe2x80x9cnon-printxe2x80x9d direction (back into a xe2x80x9ccatcherxe2x80x9d).
Asymmetrically applied heat results in steam deflection, the magnitude of which depends upon several factors, e.g. the geometric and thermal properties of the nozzles, the quantity of applied heat, the pressure applied to, and the physical, chemical and thermal properties of the ink. Although solvent-based (particularly alcohol-based) inks have quite good deflection patterns, and achieve high image quality in asymmetrically heated continuous ink jet printers, water-based inks until now, have not. Water-based inks require a greater degree of deflection for comparable image quality than the asymmetric treatment, jet velocity, spacing, and alignment tolerances have in the past allowed. Accordingly, a means for enhancing the degree of deflection for such continuous ink jet systems, within system tolerances would represent a surprising but significant advancement in the art and satisfy an important need in the industry for water-based, and thus more environmentally friendly inks.
According to a feature of the present invention, a continuous ink jet printhead includes an ink delivery channel. A plurality of nozzle bores are in fluid communication with the ink delivery channel. An individual obstruction is associated with each nozzle bore. Each individual obstruction is positioned in the ink delivery channel such that each obstruction creates a lateral flow pattern in ink continuously flowing through each of the plurality of nozzle bores as measured from a plane perpendicular to the plurality of nozzle bores.
According to another feature of the present invention, a continuous ink jet printhead includes a body, portions of the body defining an ink delivery channel, other portions of the body defining a nozzle bore, the nozzle bore being in fluid communication with the ink delivery channel. An obstruction is positioned in the ink delivery channel such that the obstruction creates a lateral flow pattern in ink continuously flowing through the nozzle bore as measured from a plane perpendicular to the nozzle bore.
According to another feature of the present invention, a method of enhancing ink deflection in a continuous ink jet printhead includes providing a continuous flow of ink through a nozzle bore; creating a lateral flow pattern in the ink; and causing the ink to deflect as the ink flows through the nozzle bore.